Communication system



July 26, 1932. P. H. EVANS COMMUNICATION SYSTEM Original Filed Sept. 24, 1923 ATTORNEY Patented July 26, 1932 UNITED I STATES PATENT OFFICE PORTER H. EVANS, OF BROOKLYN, NEW YORK, ASSIGNOB TO WmTERId ELECTRIC COM- PANY, INCORPORATED, OF NEW YORK, N. Y A CORPORATION NEW YORK COMMUNICATION SYSTEM Original application filed September 24, 1928, Serial No. 664,488, now ratent No. 1,786,852, and in Germany August 15, 1924. Divided and this application filed October 19, 1928. Serial No. 400,840. Renewed Inch 25, 1932.

This invention relates to carrier wave communication systems and particularly to the control of the' transmission level 1n carrler Wave systems.

The application is a division of original application Serial No. 664,432, filed September 24, 1923, patented November 26, 1929, #1,736,852.

One object of the invention is to provlde a, repeating circuit employing thermionic vacuum tubes that shall gradually and continuously vary the impedance of one of the tubes in an improved manner without any moving parts to control the gain in transmission level.

Another object of the invention is to provide a repeating circuit of the above indicated type that shall control the amplifying factor of one tube according to the output current of another tube without generating undesired oscillatory currents.

A further object of the invention is to provide a carrier wave receiving circuit having space discharge devices connected'in tandem to an incoming line that shall control the impedance of one of the devices according to the output of anotherdevice and prevent generation. of spurious oscillations.

In repeating circuits and in carrier wave receiving circuits it is desirable to control the energy level transmitted to the receiving ap paratus. The control of the energy level should be gradual and continuous without generating any undesirable oscillatory currents.

The present invention is illustrated by means of a receiving circuit for a. carrier wave transmission system. Two three-element thermionic amplifier tubes and a detector or rectifier tube are connected in tandem to an incoming line. The incoming line supplies carrier waves of widely diifering intensity to the amplifier tubes for calling and communication purposes.

A resistance element which is included in the output circuit of the rectifier or detector tube is also included in the grid circuit of the two amplifier tubes. The resistance element thus impresses a potential on the grids of the amplifier tubes which varies according to the output from the rectifier or detector tube.

A condenser is shunted across the anode and cathode of the rectifier or detector tube to by-pass any carrier frequency waves which may pass through the detector tube. A filter element comprising condenser and resistance elements is connected across the gain control resistance element for shunting speech frequency variations to prevent the amplifier tubes from setting up spurious oscillations. If the filter were not connected across the gain control resistance element, undesirable oscillations might be amplified to cause socalled singing.

The single figure in the accompanying drawing is a diagrammatic view of a receiv ing channel provided with a gain control circuit constructed in accordance with the invention.

Referring to the drawing an incoming line comprising conductors 1 and 2 supplies carrier waves of varying amplitude to an amplifier 3 comprising space discharge devices 4 and 5. The incoming line is connected to the space discharge device 5 by means of a transformer 6 and the space discharge device 5 is connected to the device 4 by means of a transformer 7. Each of the devices 4' and 5 comprises an anode, a cathode and a grid or control element.

A detector or rectifier space discharge de-,

vice 8 is connected to the output circuit of the space discharge device 4 by means of a transformer 9. The output circuit of the detector tube 8 is connected by a transformer 10 to an operators telephone set (not shown) or by a rela 11 to a selective calling means (not shown Switch elements 12 and 13 provide a shunt circuit around the relay 11 when the operators telephone set is in service. Inasmuch as the invention is not concerned with the operation of the selective calling circuits and the operators telephone set, a detailed .description and illustration thereof is deemed unnecessary. The calling circuits and the operators telephone set are fully illustrated in the original application Serial No. 664,432, filed September 24, 1923.

A battery 14 is heating current to t e filaments of the space rovided for supplying discharge devices 8, 4 and 5. A battery 15 is provided for supplying plate potential to the space discharge devices 4 and and a battery 16 is rovided for supplying plate 5 potential to t e dectector or rectifier discharge device 8. A battery 17 supplies negative grid potential to the detector or rectifier device 8 and a battery 18 supplies negative grid potential to the space discharge devices 4 and 5.

5. Thus, a negative potential is impressed on the grids of the discharge devices 4 and 5 which varies in accordance with the space current of the detector or rectifier space discharge device. A filter comprising a resistance element 20 and condensers 21 and 22 is connected across the resistance element 19 for shunting voice frequency variations to prevent the amplifier 3 and the detector or rectifier acting as an oscillation generator. The filter insures against the generation of spurious oscillations which would cause the so-called singing. The filter also serves to adjust the time constant of the circuit to the desired value. A condenser 23 is connected between the plate and filament of the detector or rectifier space discharge device 8 to by pass any high frequency carrier waves which may pass through the detector or rectifier discharge device.

The carrier waves of varying amplitude supplied by the incoming line comprising conductors 1 and 2 are amplified by the discharge devices 4 and 5 and rectified by the discharge device 8. The output circuit of the discharge device 8 may be traced from the plate of the device 8 through the primary winding of the transformer 10, relay 11, battery 16, gain control resistance 19 and ground to the filament of the discharge device 8. It is thus apparent that a potential is im pressed across the gain control resistance 19 which varies according to the output from the detector or rectifier discharge device 8.

- The gain control resistance element 19 is also included in the input circuits to the amplifier space discharge devices 4 and 5.

The input circuit for the discharge device 5 may be traced from the grid of the device 5 through the secondary winding of the transformer 6, grid biasing battery 18, filter, the gain control resistance element 19 and ground to the filament of the discharge device 5. The input circuit for the space discharge device 4 is traced in a like manner through the secondary Winding of the transformer 7. It is thus apparent that an increase in the space current of the detector or rectifier discharge device 8 will increase the negative potential impressed on the grids of the amplifier discharge devices 4 and 5, This will serve (90 reduce the amplitude of the waves su plied discharge devices 4 and 5 are connected.

Moreover, the grid of the detector or rectifier discharge device 8 may alone be thus connected and the grids of the discharge devices 4 and 5 may be connected to ground through an invariable biasing battery.

Modifications in the system and in the arrangement and location of parts may be made within the spirit and scope of the invention and such modifications are intended to be covered by the appended claims.

What is claimed is:

1. In a repeater system, a plurality of space discharge repeaters arranged in tandem, an anode-cathode circuit for one of said repeaters including a resistance, said resistance being included in the id cathode circuit of a second one of sald repeaters for said tubes including a resistance element, said resistance element being inc uded in the gridcathode circuit of another of said tubes, and a filter element connected across said resistance element for shunting alternating currents to prevent singing condition in the system.

3. In a carrier wave receiving system, two high-frequencyamplifier tubes and a rectifier tube connected in tandem to an incoming line, each of said tubes comprising a grid, a cathode and an anode, and a resistance element connected in the output circuit of said rectifier tube and the input circuits of the two amplifier tubes for gradually and continually governing the amplifying power of saidamplifier tubes according to the output current from said rectifier tube.

4. In a signal system, a plurality of space discharge tubes arranged in tandem, each of said tubes having a grid, a cathode and an anode, one of said tubes serving as a detector, a resistance element in the output circuit of said detector tube, said resistance element being included in the grid-cathode circuit of another one of said tubes to form a gain con- 7 trol circuit, and a filter element connected to said resistance element for preventing generation of undesired oscillatory currents in the system and for adjusting the time constant oi the gain control circuit.

5. In a repeater system, a plurality of space discharge repeaters arranged in tandem, an anode-cathode circuit for one of said repeaters including a resistance, said resistance being included in the grid cathode circuit of another of said repeaters, and a filter element connected across said resistance consisting of capacity and resistance elements adapted to shunt around said resistance alternating currents whereby the setting up of continuous oscillations in said repeater system is prevented.

6. In a carrier wave receiving system, two high-frequency amplifier tubes and a rectifier tube connected in tandem to an incoming line, each of said tubes comprising a grid, a cathode and an anode, a resistance element connected in the output circuit of said rectifier tube and in the input circuit of one of said amplifier tubes for gradually and continually governing the amplifying power of 4 the system according to the output current from said rectifier tube, and a filter element connected across said resistance element for shunting alternating currents to prevent singing condition in the system.

7. In a carrier Wave receiving system, a high frequency amplifier tube and a detector tube connected in tandem to an incoming line, each of said tubes comprising a grid, a cathode and an anode, a resistance element connected in the output circuit of said detector tube and in the'input circuit of said amplifier tube for gradually and continually governing the amplifying power of the system according to the output currentfrom said rectifier tube, a condenser connected between the anode and cathode of said detector tube for by-passing carrier frequency waves, and a filter element comprising capacity and resistance elements connected across said first mentioned resistance element for shunting alternating currents to prevent singing condition in the system.

8. In a signal system, a space discharge device provided with input and output circuits and adapted to have relatively low frequency currents and a high frequency carrier current in the output circuit, a resistance stricted frequency range of the currents in the output circuit of said device.

10. A gain control circuit comprising in combination, an amplifier having a gridcathode circuit, a rectifier connected in tandem with said amplifier, a resistance element carrying rectified current from said rectifier, means for connecting said resistance element to said grid cathode circuit of the amplifier to control the gain of the amplifier, and means for shunting said resistance element to control the time constant of the gain control circuit.

11. A gain control circuit comprising in combination, a repeater having a grid-cathode circuit, a rectifier connected in tandem with said amplifier, a resistance element car rying rectified current from said rectifier, said resistance element bein included in the grid-cathode circuit of said repeater to control the gain of the repeater, and a filter element connected to said resistance element for preventing the generation of undesired oscillatory currents in the system and for adjusting the time constant of the gain control circuit.

12. A gain control circuit comprising in combination, an amplifier having input and output circuits, a rectifier connected to the output circuit of said amplifier, a resistance element in circuit with said rectifier, said resistance element beln included 1n the 1nput circuit of said amplifier, and a filter conelement included in the output circuit, means i for governing the input level to said device according to the potential across said resistance element, and a filter connected across said resistance element for shunting the low frequency currents.

9'. In a signal system, a space discharge device provided with input and output circuits and adapted to have currents of different frequencies in the output circuit, a resistance element included in the output circuit, means for governing the input level to said device according to. the potential across said resistance element, and selective means for limiting the control of the potential across said resistance element to a re- 

